The present invention relate generally to a semiconductor manufacturing apparatus and, in particular, to a semiconductor manufacturing apparatus having a vertical furnace and a boat cover thereof.
Semiconductor devices are manufactured through processes such as depositing thin films on surfaces of silicon wafers and etching the latter. Such thin film deposition and etching are carried out in a semiconductor manufacturing apparatus having a vertical furnace.
In recent years, the degree of integration of integrated circuits as in semiconductor devices has been increasing. This caused the relevant processing or working to be more fine and precise. The increased integration requires the thin film deposition in the semiconductor manufacturing apparatus to be performed such that the resulting semiconductor devices have improved uniformity in film thickness and homogeneity.
In the vertical furnace, a multitude of wafers, that is, substrates to be processed, are subjected to a required treatment while they are retained horizontally by means of a boat. The boat is covered by a boat cover so as to improve the uniformity in thickness of the film deposited on the wafers.
Reference is made to FIGS. 13 and 14 hereof in which a conventional semiconductor manufacturing apparatus is shown.
In these figures, reference numeral 1 designates an outer tube with a closed upper end. The outer tube 1 includes a short tubular flange 2 airtightly connected to a lower end thereof. An inner tube 3 with upper and lower opened ends is supported by the flange 2 and disposed internally of the outer tube 1 concentrically therewith. An introducing nozzle 6 communicates with the flange 2 for introducing a reactive gas into the outer tube 1. An exhaust nozzle 7 communicates with a gap defined between the outer tube 1 of the flange 2 and inner tube 3. Extend around the outer tube 1 is a heater 4.
Lower end of the flange 2 is airtightly covered by a seal cap 5, on which a cover boat 10 is vertically disposed. The cover boat 10 serves as a boat for retaining wafers horizontally in a multi-storied fashion and forms part of a boat cover tube 8 to be described below. The cover boat 10 has a lower base 17, a support post 11 and a cover plate 12. The post 11 is disposed vertically on the lower base 17 and has horizontally extending grooves or recesses for retaining wafers. The cover plate 12 is disposed vertically and takes the form of a semicircle so as to provide a slit gap 18. The wafers are loaded on the cover boat 10 and introduced into the inner tube 3 for required processing.
For processing the wafers, the inside of the furnace is heated by the heater 4, followed by introducing a reactive gas by means of the introducing nozzle 6 and exhausting through the exhaust nozzle 7. The introduced reactive gas is decomposed by heating and deposited as thin films through reaction with the wafer surfaces. Upon deposition of these thin films, the flow of the reactive gas imparts a significant influence on the quality of the thin film deposition, e.g., uniformity of the thin films. Consequently, it is necessary for all wafers to be fed with a uniform reactive gas stream.
To cope with such problem, the conventional vertical furnace has the above-mentioned boat cover tube 8 with the slits 18.
Boat cover tube 8 is divided into left and right halves by a boat cover 9 and a cover boat 10. The boat cover 9 has an upper base 15 with a central aperture 16. The upper base 15 is provided with the cover plate 12 having an arc-shaped cross section and a vertical length which is substantially equal to the height of the boat. Between adjacent cover plates 12, 12, there is provided a slit gap 18 extending vertically. Auxiliary cover plate 14 having the same width as that of the slit gap 18 is provided in an opposed relation to the slit gap 18 by means of pieces 13. Between the auxiliary cover plate 14 and the cover plate 12, there is provided a predetermined clearance or gap extending radially. A semi-cylindrical cover is thus provided by the cover plate 12 and the auxiliary cover plate 14.
The boat cover 9 is introduced into the inner tube 3. The upper base 15 is loaded onto the upper end of the inner tube 3, whereby the boat cover 9 is retained by the inner tube 3.
The cover boat 10 has substantially the same arrangement as that of the boat cover 9. The lower base 17 has a support post 11 disposed vertically thereon. On the post 11, there is provided a cover plate 12 having a arc-shaped cross section and a vertical length substantially equal to the boat height in such a manner as to provide a vertical gap 18 in the form of a slit. An auxiliary cover plate 14 of the same width as the slit gap 18 is disposed in opposed relations to the slit gap 18. A given gap is provided between the auxiliary cover plate 14 and the cover plate 12. The cover boat 10 is disposed vertically on the seal cap 5. The post 11 has a plurality of grooves or recesses (not shown) disposed at a predetermined pitch, which is designed for retaining the wafers in a horizontally oriented fashion.
Boat cover 9 is disposed within the inner cover 3 and the cover boat 10 can be inserted into and taken out from the inner tube 3 with the wafers loaded thereon. When the cover boat 10 with the wafers loaded thereon is introduced into the furnace, that is, the inner tube 3, the boat cover tube 8 of cylindrical configuration is defined by the boat cover 9 and cover boat 10, whereby the wafers (not shown) are enclosed by the boat cover tube 8.
Reactive gas fed from the introducing nozzle 6 flows into the inner tube 3 and rises between the inner tube 3 and the boat cover tube 8. While rising, the reactive gas passes through a gap between the auxiliary cover plate 14 and the cover plate 12 and through the slit gap 18 and flows into the boat cover tube 8 (see FIG. 14) and around the circumferential portions of the wafers. The gas rises further and flows out through the aperture 16. It then descends between the outer tube 1 and inner tube 3 and is exhausted through the exhaust nozzle 7.
By provision of the boat cover tube 8, the reactive gas flows between the boat cover tube 8 and inner tube 3 and through the inside of the boat cover tube 8, and is then diffused at the slit gap 18. Thereafter, it flows into the boat cover tube 8, whereby the wafers are rendered to have thin films of improved uniformity in thickness at the circumferential and central portions thereof. The auxiliary cover plate 14 is an obstructive plate for obstructing the flow of the reactive gas from the slit gap 18 directly into the boat cover tube 8 to thereby achieve effective diffusion of the reactive gas.
Another method for improving the uniformity in thickness and homogeneity of thin films deposited on wafers is known wherein a gap between a tubular member enclosing the wafers and the peripheral edges of the wafers is reduced.
Reference is now made to FIGS. 15 and 16 hereof wherein an example of such semiconductor manufacturing apparatus without the cover boat tubular member 8 is shown. In this apparatus, a gap between the tubular member enclosing the wafers and the peripheral edges of the wafers is reduced to improve the uniformity in thickness and homogeneity of thin films deposited on the wafers.
In FIGS. 15 and 16, the same reference numerals are used for portions which are also shown in FIGS. 13 and 14.
The outer tube 1 has a lower end to which a flange 2 in the form of a short tube is airtightly connected. An inner tube 3 supported by the flange 2 and having upper and lower opened ends is disposed within the outer tube 1 concentrically therewith. An introducing nozzle 6 communicates with the flange 2 for introducing a reactive gas into the outer tube 1. An exhaust nozzle 7 is provided to communicate with a gap between the outer tube 1 of the flange 2 and the inner tube 3. Around the outer tube 1, there is provided a heater 4. A boat 19 is vertically disposed on a seal cap 5 covering the lower end of the flange 2 airtightly. The boat 19 is designed to horizontally retain wafers in a multi-storied fashion. The wafers 32 are loaded on the boat and are fed into the inner tube 3 for a required treatment.
In the example apparatus, the inner tube 3 is provided with an escape portion 3a so as to reduce the gap "t" between the tubular member or the inner tube 3 and the peripheries of the wafers. By providing the escape portion 3a, the interference between the inner tube 3 and a support post 19a of the boat 19 can be avoided, whereby the reduction of the gap "t" is enabled and the uniformity in thickness and homogeneity of the thin films are improved.
Thickness of the thin films deposited on the wafers is highly influenced by the flow of the reactive gas. Thus, the wafers are enclosed by the boat cover tube as in the prior apparatus shown in FIGS. 13 and 14. However, in the above-mentioned example apparatus, a problem is still experienced such that the film thickness adjacent to the slit gap is liable to become large or small. Thus, it is required to improve the uniformity in film thickness in the vicinity of the slit gap.
There is also a demand that the number of wafers which can be treated at one time be increased to enhance the productivity of a semiconductor manufacturing apparatus. A semiconductor manufacturing apparatus in which wafers are treated in its vertical furnace experiences a height restriction that is up to the height of the ceiling of a clean room. Thus, it is not possible to make the boat or vertical furnace unconditionally high. This requires the wafers supported on the boat to be positioned at a small pitch but it is known that by making the pitch between the wafers small, the film thickness around the slit gap is liable to become irregular.
Further, when film deposition process is carried out, reaction by-products stick to a reaction chamber. Before long, the reaction by-products come off in the form of particles and stick to the wafers and contaminate the latter, thus deteriorating the treatment quality. It is therefore necessary to clean the outer tube 1 and inner tube 3 forming the reaction chamber periodically or after a predetermined period of operation time.
Moreover, where the boat cover tube is provided to improve the quality of thin films to be deposited on wafers as described above, the inside arrangement of the furnace becomes complex, thus necessitating a prolonged time for cleaning. This further leads to the problem that the semiconductor manufacturing apparatus needs to be interrupted for a longer time period, deteriorating the production efficiency of the semiconductor manufacturing apparatus.
In the separate conventional apparatus shown in FIGS. 15 and 16, the uniformity in film thickness and homogeneity is improved without the use of the boat cover tube. However, since the reactive gas is arranged to flow upwardly from below within the inner tube 3 and the gap "t" between the peripheries of the wafers and the inner surface of the inner tube 3 is small, the exhaust conductance relative to the gas exhaust is large, thus producing a pressure difference between upper and lower portion of the reaction chamber. Pressure of the reactive gas is an important film deposition condition determining factor. Thus, it becomes necessary to provide a temperature gradient of 50.degree. C. between the upper and lower portions of the reaction chamber. The temperature difference influences the quality of the deposited films and hence is undesirable in terms of the uniformity of the thin films.